Catherine L. Guerriero, a 43-year-old adjunct education and politics professor at Teachers College, Columbia University and New York University, registered as a Democrat in New York in 1988. But she did not vote in 2009, 2005 and 2001, the three years that included races for public advocate.

Like many registered voters, she voted in general elections in 2012, 2010 and 2008 and a primary in 2012. But she did not cast a vote in any election over an eight-year stretch, from 2000 to 2008.

During Sunday’s televised debate sponsored by the Wall Street Journal, WNBC-TV and Telemundo, Ms. Guerriero said that she had “no good answer” for why she did not vote.

“People died so that we could vote. This is an extraordinary gift,” she said. “And there is no good answer to that other than it didn’t happen.”

She added that, in the past, she has gotten “very focused” with work.

Reshma Saujani, a 37-year-old Wall Street lawyer-turned-deputy public advocate, moved to New York in 2002 to work at a law firm after getting a master’s degree at Harvard University and a law degree from Yale University. But two sets of city voting records, one obtained from the Board of Elections and the other provided by her campaign, suggest Ms. Saujani did not vote in the 2005 citywide elections.

Ms. Saujani’s campaign produced documents showing that she registered to vote in New York in 2003 and blamed a spelling error for the discrepancy with her current official record, which says Ms. Saujani did not register until 2006.

But the documents only show that Ms. Saujani cast a ballot in 2004, not in 2005, when former Public Advocate Betsy Gotbaum defeated civil rights activist Normal Siegel in the Democratic primary and ran unopposed in the general election. Her campaign did not respond to requests for comment about the 2005 votes.

When asked about her voting record during the debate, Ms. Saujani said that she did not know if she was going to stay in New York City when she first moved to work on Wall Street in her 20s.

“I thought I might go back and move home to Chicago because I was helping out my parents during a tough time,” she said. “And I fell in love with New York. And I chose to stay here, to get active here, to organize people here, and I decided to register to vote.”

A copy of Ms. Saujani’s personal income tax returns from 2002 to 2006 show that she lived in Midtown Manhattan during that time. She voted in all three elections in 2009, the year before she was an unsuccessful Democratic congressional candidate against U.S. Rep. Carolyn Maloney (D-N.Y.).

Daniel Squadron, a 33-year-old New York state senator since 2008, has voted in most elections since he became a registered Democrat at age 18 in 1998. But city records show he did not vote in the 2005 or 2001 primaries.

During Sunday’s debate, Mr. Squadron said he was “surprised” by records showing he had not voted in 2005 since he had been working on city political campaigns at the time.

He did vote in the general elections and a special runoff vote in 2001, the records show.

City voting records are not fool proof and can have errors.

Ms. James, 54 years old and a New York City Council member since 2003, voted in every primary, runoff and general election during the 2001, 2005 and 2009 cycles, the documents showed.

Three of the candidates also said they were unsure of who they were voting for in the Democratic primary for mayor. Ms. Guerriero said she was planning to vote for former city comptroller Bill Thompson. Mr. Squadron and Ms. Saujani said they had not decided who they were voting for and might not disclose their eventual choice. Ms. James said she would disclose who she voted for.

New York City good government groups lashed out at candidates who failed to vote in more than a few city elections, saying missed votes equate to a poor grasp of the issues.

Susan Lerner, executive director of Common Cause New York, a nonprofit citizens’ advocacy group, said she does not look for a “perfect lifetime record” of voting from political candidates but a consistent pattern of votes over several years. More than a few missed elections are a red flag, she said.

“It raises questions about their engagement in the issues that they want to be responsible for,” Ms. Lerner said. “It’s not a good model for the voters to convince them to vote in citywide elections.”

Dick Dadey, executive director of Citizens Union, a government and political civic group, said youth (Ms. Saujani was 26 when she first moved to New York) or a maverick political brand (Ms. Guerriero prides herself on her lack of support from the Democratic Party establishment) are not reasons to skip voting.